On the Atheist Prayer Experiment Facebook page, quite a few participants have mentioned that praying for people/situations feels pointless, and that they would feel much better if they did something practical. I agree.
I remember when I was in hospital having tests, at the time when it was becoming clear that my first kidney transplant was failing. My mother - a lovely woman and a Christian, but not the most subtle individual - asked some of my Christian friends why they had not been to visit me. When they objected that they had been praying for me, she said "Big deal". Truth is, I felt a lot more love from the people who bothered to stump up at hospital or took me out for a coffee and listened to me unload. You prayed for me? Yeah - big deal.
A phrase from my old Christian days has been running through my head: "God has no hands on earth but yours".
Christians: do you think you ever pop a two-minute prayer heavenward because it makes you feel like you've done something to help but actually it costs you nothing? I'm pretty sure I was sometimes guilty of that back when I was a Christian.